They warn that "high caffeine users", those who drink more than the equivalent of seven cups of instant coffee a day, are at the increased risk.

But because of the extra caffeine content in brewed coffee only half as many cups are needed to create the same effect.

Even moderate amounts of the stimulant can lead people to hear voices and see things that are not there, the researchers warn.

Previous studies have shown that too much caffeine can lead to heart palpitations, insomnia and even affect a woman's chances of becoming pregnant.

Simon Jones, from Durham University, who led the study, said: "Some people have hallucinations which they find frightening, others say they often hear voices and it does not appear to affect their everyday lives.

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"What our study has shown is a clear link between these hallucinations and a high caffeine intake."

Although the connection between hearing voices and large amounts of caffeine has been suggested before, Mr Jones said that results of earlier research had been mixed.

The new study also showed that people who had a high caffeine intake were not more likely to think that others were out to get them, a so-called "persecution complex".

Previous studies have suggested that at some point in their lives up to 10 per cent of people will hear voices, which are not necessarily a sign of mental illness.

Researchers looked at the caffeine intake of 200 students, some of whom had experienced seeing things that were not there, hearing voices or sensing the presence of the dead.

The volunteers were questioned about their caffeine intake from products including coffee, tea, energy drinks, chocolate bars and caffeine tablets.

Researchers found that "high caffeine users", those who had more than the equivalent of seven cups of instant coffee a day, were three times more likely to have had hallucinations than those who had less than the equivalent of one cup.

Those who have three cups of brewed coffee a day could be at the same risk, they warn, because of the drink's higher caffeine content.

On average the volunteers had the equivalent of three cups of instant coffee a day, which could still cause an increased risk, according to the study.

The researchers believe that caffeine could heighten the effect that stress has on the body, triggering the hallucinations.

However, they also suggest that people who are more prone to hallucinations could also be more stressed and more likely to consume large amounts of caffeine.

They plan to carry out more research into the effects of diet on hallucinations to discover whether other foodstuffs, such as sugar, can also trigger the episodes.

The findings of the study, funded by the Economic and Social Research Council and the Medical Research Council, are published in the journal Personality and Individual Differences.